chayav inish livisumay- Simply put the average salary for a physician and attorney is double or triple what the average Rebbi makes. Not to say that there arent professionals with out jobs, but lets focus on the average. The average Rebbe also has more children. So even if they find a job, it will most likely not cover there expenses.
On a Rebbe’s salary, after taxes, mortgage, insurance, tuition, transportation etc… there is almost nothing left for food, clothing and any extras.
I second what Bowwow said- valid hishtadlus needs to be made, and one shouldnt say that he will be different than the trend and be self sustained on one Rebbe salary
real-brisker- Did you know that many of the Tannoim, Amoraim, Rishonim etc.. had other professions?